This article was reported by Christopher Drew, Jo Thomas and Don Van Natta Jr., and was written by Mr. Van Natta.

WASHINGTON, Oct. 20 — After 40 days of the most aggressive criminal investigation in American history, federal law enforcement officials have arrested 830 people but have failed to develop evidence that anyone now in custody was a conspirator in the Sept. 11 terror attacks.

Despite pursuing more than 365,000 tips from the public, senior investigators in the United States acknowledged that most of their promising leads for finding accomplices and some of their long-held suspicions about several suspects have unraveled.

Beyond that, none of the nearly 100 people still being sought by the Federal Bureau of Investigation is seen as a major suspect, law enforcement officials said. "There is no one in that group that I'd want someone to wake me up at 3 o'clock in the morning to tell me about," a government official said.

Investigators' latest hope for a break was dashed late this week in Chicago. On Oct. 11, the arrests of nine Egyptian men living in Evansville, Ind., had sent ripples of excitement through law enforcement circles. Two senior law enforcement officials said there was speculation that the men were an Al Qaeda cell plotting a terrorist attack.

Federal authorities had learned that one of the men had recently taken flying lessons and that they lived together in Indiana and sent money home to Egypt, a law enforcement official said. The men were sent to Chicago for questioning, but on Thursday night, with investigators' suspicions evaporating, seven of the nine were released. One was still in custody and another faced only immigration charges.

One of the men released, Tarek Albasti, 29, a part owner of the Crazy Tomato restaurant in Evansville, had been arrested while making a pot of spaghetti during the dinner rush that night. As it turned out, the flight lessons that apparently made him appear suspicious were a gift from his father-in-law, a lawyer and former United States diplomat who is also a pilot.

The widespread arrests began the day of the terrorist attacks, and the numbers mounted as agents tracked down people through logs of the hijackers' cellphones, through interviews with their neighbors and through tips phoned in or sent to the F.B.I.'s Web site. But none of those arrested have been accused of playing a supporting role in the hijackings. Most are being held on unrelated immigration violations, traffic violations or charges of falsifying documents, prompting complaints from civil rights advocates and immigration lawyers.

But the arrests have a purpose beyond the investigation of the Sept. 11 attacks: to prevent more attacks. On that score, officials say the detentions have been much more successful.

Senior government officials say they believe they have captured at least 10 members of Osama bin Laden's network, Al Qaeda, who may have been involved in cells planning other attacks. While there is no firm evidence of specific plots that have been thwarted, one senior law enforcement official said, "We know we've changed the atmosphere."

Officials also say that they believe arrests in other counties since Sept. 11 have disrupted planned attacks.

Investigators say they know the hijackers received financial and logistical support from a small group of Al Qaeda lieutenants outside the country, and the investigation has increasingly focused overseas. But, one senior government official said, "We have seen no evidence of a big network here that helped them out."

The search for potential conspirators in this country has centered on nearly 20 material witnesses who are believed to have important information and have been brought to Manhattan for detention. But in recent weeks at least nine of them have been released from jail, officials said, and those still in custody are not cooperating.

"We are getting into squeeze time," a senior official said. "We are getting them before grand juries and confronting them with financial records and phone records, and it will be harder for some people to dodge and weave."

In the last 10 days, two men have been charged with lying to the grand juries investigating the attacks. One was charged in Phoenix with giving false statements to the federal investigators about his association with Hani Hanjour, the hijacker believed to have piloted the jet that crashed into the Pentagon. A Jordanian man attending college in California was charged with making false statements describing his association with two other hijackers, Nawaf Alhazmi and Khalid Almihdhar.

The charges allow the authorities to keep the men in jail while they continue to investigate. But law enforcement officials say there is no evidence either man had advance knowledge of the Sept. 11 plot. Investigators have established connections between the hijackers and about two dozen people now in custody, although those connections are only casual.

Shortly after the hijackings, the F.B.I. thought it had stumbled onto a cell of young Arab men in San Diego who might have helped two of the hijackers. The agency became interested in at least five men, most of them college students, through a tantalizing lead: the first name and the phone number of one of them, Osama Awadallah, was found scrawled on a piece of paper in the 1988 Toyota Corolla that Mr. Alhazmi, had left in a parking garage at Dulles International Airport in Virginia on Sept. 11 before boarding American Airlines Flight 77, which hit the Pentagon.

Federal agents learned that some of the men had roomed at the same Muslim leader's house in San Diego as Mr. Alhazmi and his fellow hijacker, Mr. Almihdhar. Some, including Mr. Awadallah, also had worked at a gas station where Mr. Alhazmi was briefly employed last year. And Mr. Alhazmi, as a favor, had included one of the students, Yazeed Alsalmi, on his auto insurance for two months in late 2000 to help him get a lower rate.

The F.B.I. arrested the five men and rushed them to New York to be held as material witnesses, prompting complaints from Randall B. Hamud, the lawyer for three of them, who said they were being tarred with guilt by association.

Send us in confidence details of cases where you think
Organized Freemasonry has personally hurt yourself,
family, friends, aquaintances, or community. We would
also appreciate any additional background information,
links, and references on Freemasonry and the Occult.
Help us take a bite out of Freemasonry.